1. Field of the Invention
The present invention relates to a closed type motor-driven compressor and, more particularly, to a closed type motor-driven compressor employed for air conditioning or refrigerating an suitable for improving a performance of a refrigerating cycle and securing a reliability of the compressor.
Furthermore, the present invention is directed to a closed type motor-driven compressor based on a double-bearing structure intended to avoid a concentration of sliding load.
Moreover, the present invention is concerned with a scroll compressor suitable mainly for improving strength of wraps for forming a pump and obtaining a high air tightness. Additionally, the present invention relates to an end mill for machining wraps of a fixed scroll and an orbiting scroll in the scroll compressor.
2. Description of the Prior Art
In the scroll compressor shown in FIG. 4, a compression mechanism 7 is accommodated in an upper portion of the closed container 9, while a motor 8 is accommodated in the lower portion thereof. Contained in the closed container 9 is a lubricating oil for lubricating sliding portions of the compression mechanism 7.
The compression mechanism 7 includes a fixed scroll 7a, an orbiting scroll 7b, a frame 14, a crankshaft 11, an Oldham's ring 7c. The motor 8 has a stator 8a and a rotor 8b. The stator 8a is fixed by shrinkage-fitting in the closed container 9. The rotor 8b is fixed by press-fitting to the crankshaft 11.
An outer peripheral part of the frame 14 is fixed to the 10 closed container 9 and provided with a bearing for the crankshaft 11. The fixed scroll 7a is fastened to the frame 14.
The fixed scroll 7a and the orbiting scroll 7b respectively have spiral wraps extending from end plates. The respective wraps mesh with each other, thus defining compression chambers.
An eccentric part of the crankshaft 11 is rotatably received in a boss of the orbiting scroll 7b. A rotation of the scroll 7b about its own axis is prevented by the Oldham's ring 7c, whereby revolving action is given. The arrangement is such that a refrigerant gas, suctioned for an inlet (not shown) of the fixed scroll 7a is gradually compressed in the compression chambers upon rotation of the orbiting scroll 7b.
The lubricating oil 10 is supplied to a bearing part 12a, crank part 12b, etc. with rotations of the crankshaft 11 connected directly to the rotor 8b. The lubricating oil is thereafter discharged through a discharge port 13 and returned to the closed container bottom part 9a. Some of the lubricating oil, however, is atomized due to an influence of stirring or the like of the rotor 8b of the motor module. The refrigerated gas enters the compression mechanism from a suction pipe 4b and is compressed therein. The compressed gas is exhausted into the closed container 9 from the discharge port 13 and fed together with the atomized lubricating oil to the refrigerating cycle via discharge pipe 4a.
The prior art refrigerating cycle illustrated in FIG. 5 includes a compressor 1, heat exchangers 2a, 2b, an expansion member 3 and a piping system 4 for connecting these components, thereby circulating the refrigerant. The oil separator 5 separates the atomized lubricating oil discharged together with the refrigerant from the discharge pipe 4a of the compressor 1. The oil separator 5 is equipped with a bypass line 6 for quickly returning only the lubricating oil component for the compressor (interior). With this arrangement, the reliability of the compressor is improved by preventing a deficiency of lubricating oil within the compressor. At the same time, the lubricating oil is prevented from circulating through the heat exchangers, thereby preventing a drop in efficiency of the refrigerating cycle as well as preventing a decrease in heat transfer coefficient due to an adhesion of lubricating oil to an internal wall of the heat exchanger pipe.
The following problems are inherent to the prior art constructions. Provided outside the compressor is an oil separator circuit for quickly returning to the compressor the lubricating oil discharged from the compressor discharge pipe to the refrigerating cycle. The structure of the refrigerating cycle becomes complicated and is increased in size, resulting in an increase of the total cost of the system. Then, the following measures are taken in some cases, the oil separator circuit is not provided, and, instead, as illustrated in FIG. 6, a discharge pipe 4A is provided in a vicinity of the center of the container. A quantity of the lubricating oil is reduced by increasing the refrigerant component to be fed outside the compressor as in the case of centrifugally separating the lubricating component having a large density caused by a swirling flow due to the rotor 8b of the motor.
In this case, the centrifugally separated lubricating oil is re-atomized by the rotor of the motor and, hence, a gas-liquid separating ability is insufficient. The lubricating oil within the compressor becomes sufficient, resulting in a reduction in the reliability of the compressor.
Further, a circulating of the lubricating oil to the heat exchangers is caused. The heat transfer coefficient is reduced because the adhesion of the lubricating oil to the inner walls of the pipes of the heat exchangers and, therefore, the efficiency of the refrigerating cycle is decreased. Needed further is an air space for arranging the discharge pipe to the upper portion of the rotor. This leads to an increase in the overall size of the compressor.
Another example of a gas-liquid separation within a compressor is disclosed in Japanese Unexamined Patent Publication No. 58-160587. Based on this technical approach, a gas-liquid separation blade is provided on the upper portion of the rotor of the motor. Provided further on the upper portion of the motor is a partition plate for substantially entirely partitioning the motor and the compression mechanism. A discharge pipe is arranged to communicate with the air space in the upper portion of the partition plate. An outer periphery of the partition plate contacts with an inner wall of the closed container, while an inner periphery thereof contacts with a bearing boss. In this last mentioned prior art construction, the internal structure of the compressor becomes complicated and the costs increased. In, for example, Japanese Unexamined Patent Publication No. 1-170774, an auxiliary bearing in the conventional double-bearing-structured closed type motor-driven compressor is proposed wherein a typical ball bearing, having spherical members rotatably disposed between an inner ring and an outer ring, is press-fitted into a boss hole of a support leg formed by casting or forging, etc.
The mounting structure of the auxiliary bearing of the conventional closed type motor-driven compressor described above, however, has the following disadvantages.
Namely, the cast or forged member is poor in terms of the forming accuracy. If such a cast or forged member exhibiting the poor forming accuracy is employed as a constructive material of the support leg, equipment and expenditure for working these materials are required. This contributes to a rise in the total manufacturing costs.
Additionally, for securing an accurate center of the auxiliary bearing and the casing minor diameter which requires precise centering during an assembly, it is necessary to, as a matter of course, secure a concentricity between an annular major diameter of the support leg and the boss hole into which the ball bearing is press-fitted. The casing decreases in rigidity, and when fitting the stator of the motor, a deformation is caused. In this case also, however, it is necessary that the casing inner surface be worked to enhance the accuracy of the casing combined with the support leg. There are many disadvantages in terms of the manufacturing costs including the assembly.
Additionally, in the conventional closed type motor-driven compressor a ball roller bearing is employed as an auxiliary bearing. In products such as a domestic room air-conditioner which utilizes the foregoing closed type motor-driven compressor, an operating noise is perceived as an important factor for determining the quality thereof. It is impossible in the roller bearing to avoid a generation of tap noises attributed to the rolling of the ball bearing.
A further conventional scroll compressor is disclosed in, for example, Japanese Unexamined Patent Publication No. 1-187388, wherein wraps of the fixed and orbiting scrolls have inner and outer surfaces which basically extend from the end plates. To illustrate in more detail, the wraps commonly take the configuration shown in FIG. 22 wherein the compressor includes a fixed scroll 201, an orbiting scroll 202, wraps 203a, 203b, end plates 204a, 204b, wrap root parts 205a, 205b, stepped parts 224a, 224b, wrap tip parts 206a, 206b, chamfered parts 225a, 225b, wrap side surfaces 207a, 207b, wrap bottom surfaces 209c, 209b, and an air gap 226.
As shown in FIG. 22, the wrap root parts 205a, 205b of the wraps 203a, 203b are provided with small stepped parts 224a, 224b in order to enhance the mechanical strength of the wraps 203a, 203b. Furthermore, the wrap tip parts 206a, 206b are formed with the chamfered parts 225a, 225b which do not contact the stepped parts 224a, 224b when the fixed scroll 201 is assembled with the orbiting scroll 202.
When the orbiting scroll 202 orbits about a central axis (not shown), the wraps 203b of the orbiting scroll 202 move near to or away from the wrap 203a of the fixed scroll 201. A refrigerant gas between the wraps 203a, 203b is thereby compressed. During such operation, the arrangement is such that the refrigerant gas does not leak from the air space between the wraps 203a, 203b. The spacing between the wrap tip part 206a and the wrap bottom surface 209b, between the wrap tip part 206b and the wrap bottom surfaces 209a, 209b are minimized. Moreover, when the wraps 203a, 203b approach each other, the distance between the stepped part 224a and the chamfered part 225b and between the stepped part 224b and the chamfered part 225a are minimized so that oil films of the refrigerating machine oil mixed in the refrigerant gas are formed between the wraps 203a, 203b.
The stepped parts 224a, 224b at the root parts 205a, 205b are normally formed when machining the wraps with an end mill. More specifically, the machining of the wraps 203a, 203b is the same and, therefore, the respective portions will be shown by removing the letters a, b from the reference numerals. As illustrated in FIG. 23, in a workpiece previously formed with a wrap tip part 206 and a chamfered part 225, a wrap side surface 207 is machined by the major-diameter part of the end mill 227 (FIG. 23A). Thereafter, the wrap bottom surface 209, i.e., the upper surface of the end plate 204 is machined by the tip of the end mill 227 (FIG. 23B). The wrap 203 is thus machine by the two separate steps. However, the major diameter of the end mill 227 is set slightly smaller than the minimum spacing between the spiral wrap 203 and the end plate 204. The stepped part 224 is thereby formed simultaneously when machining the upper surface of the end plate 204 shown in FIG. 23B.
As shown in FIG. 24A, in a workpiece 229 of fixed scroll 201 or a rotary scroll 202, formed substantially in predetermined dimensions, the surface of the wrap tip part 206 is premachined. Machined by a side surface machining end mill 228 is a workpiece side surface 230 of a spiral projection which will turn out a wrap of the workpiece 229. A wrap 203 is formed so that a thick dimension of this projection is set in a predetermined dimension. Thereafter, as shown in FIG. 24B, the tip edge of this projection is cut to form an obliquely chamfered part 225 by a chamfering cutter 231.
The conventional scroll wrap machining end mill is, as illustrated in FIG. 25A, made of a typical tool steel or super hard material and has a cutting edge 233 assuming such a configuration that the tip is accurately ground. Alternatively, as depicted in FIG. 25B, a coating 234 is applied to the entire surface of a base metal 232 of the end mill. This coating 234 is composed of diamond exhibiting an extremely high hardness and high melting point or a crystal of carbides of a variety of metals.
In the scroll compressor including a combination of the fixed scroll 201 and the orbiting scroll 202 having the wraps 203a, 203b formed by the above-described machining, the tips of the respective wraps 203b, 203a are formed obliquely with the chamfered parts 225b, 225a so as not to impinge of the stepped parts 224a, 224b. Therefore, even when the wraps 203a, 203b approach each other, the air gaps 226 serving as linear seals formed between the stepped part 224a and the chamfered part 225b and between the stepped part 224a and the chamfered part 225b are increased. Generally, an oil film of refrigerating machine contained in the refrigerant gas is formed in such an air gap 226. The refrigerant gas does not leak out of the above-mentioned air gap 226 due to a sealing effect of the oil. As shown above, however, if the air gap 226 is large and when the wraps 203, 203b approach each other, a pressure of the refrigerant gas therebetween is large. Hence, the oil film of the refrigerating machine oil therein is easy to break and a sealing effect cannot be obtained. For this reason, during normal operation of the compressor, the refrigerant gas which is continuously compressed leaks out of the air gap where the oil film has been broken, thereby causing a performance reduction. The electric power consumed for operation is increased and, therefore, a problem arises in terms of saving energy.
Based on the above-described working methods, the wrap side surface and the chamfered part are machined by the separate steps and, therefore, the manufacturing time, as a matter of course, is increased and production efficiency is reduced. Additionally, if machining is conducted in this way by the separate steps, and when shifting from the machining step of the wrap side surface to the machining step of the chamfered part is carried out, reattaching a tool is required. In working of a complicated configuration such as a non-curved shape, there may be easily caused positional offset between the side surface machining end mill 228 for machining the workpiece side surface 230 and the chamfering cutter 231 for machining the chamfered part 225 in FIG. 24 and, consequently, a high dimensional machining accuracy cannot be realized.
The conventional scroll wrap machining end mill 235 illustrated in FIG. 25 is flat cutter member, the tip of which is sharp thereby resulting in a chipping readily taking place. Further, in the coating end mill, the coating 234 involves the use of diamond or crystal of carbides of various metals exhibiting extremely high hardness and high melting point. These materials have different mechanical and chemical properties from that of the end mill base metal 232, so that the end mill base metal 232 is therefore difficult to join with the coating. Previous studies have been carried out in order to determine the effects of surface treatments for promoting joining of coating to the end mill base metal 232. However, such studies have found inevitable slight deviations in temperature, atmosphere, etc. during the surface treatment and coating process. Thus, the joining strength between the end mill base metal 232 and the coating 234 is quite unstable.
As a result, when a workpiece is machined by use of an end mill base metal described above, the cutting edge 233 is sharp and is therefore brought into a point-contact with the workpiece. Bi-directional cutting stress from the side and bottom surfaces of this cutting edge 233 is applied extremely largely on the tip of the cutting edge 233. Consequently, this cutting stress extremely largely acts thereon, with the result that the coating 234 is peeled. Causes is a rapid wear of the tip of the cutting edge 233 at the initial working stage. It is impossible to secure a predetermined cutting accuracy and cutting distance.